Referring to FIG. 1, there is shown a cross-section through a portion of a combustion turbine 10. The major components of the turbine are a compressor section 12, a combustion section 14 and a turbine section 16. A rotor assembly 18 is centrally located and extends through the three sections. The compressor section 12 can include cylinders 20, 22 that enclose alternating rows of stationary vanes 24 and rotating blades 26. The stationary vanes 24 can be affixed to the cylinder 20 while the rotating blades 26 can be mounted to the rotor assembly 18 for rotation with the rotor assembly 18.
The combustion section 14 can include a shell 28 that forms a chamber 30. Multiple combustors, for example, sixteen combustors (only one combustor 32 of which is shown) can be contained within the combustion section chamber 30 and distributed around a circle in an annular pattern. Fuel 34, which may be in liquid or gaseous form—such as oil or gas—can enter each combustor 32 and be combined with compressed air introduced into the combustor 32 from the chamber 30, as indicated by the unnumbered arrows surrounding the combustor 32. The combined fuel/air mixture can be burned in the combustor 32 and the resulting hot, compressed gas flow 36 can be exhausted to a transition duct 38 attached to the combustor 32 for routing to the turbine section 16.
The turbine section 16 can include a cylindrical housing 40, including an inner cylinder 42, can enclose rows of stationary vanes and rotating blades, including vanes 44 and blades 46. The stationary vanes 44 can be affixed to the inner cylinder 42 and the rotating blades 46 can be affixed to discs that form parts of the rotor assembly 18 in the region of the turbine section 16. The first row of vanes 44 and the first row of blades 46 near the entry of the turbine section 16 are generally referred to as the first stage vanes and the first stage blades, respectively.
Encircling the rotor assembly 18 in the turbine section 16 can be a series of vane platforms 48, which together with rotor discs 50, collectively define an inner boundary for a gas flow path 52 through the first stage of the turbine section 16. Each transition duct 38 in the combustion section 14 can be mounted to the turbine section housing 40 and the vane platforms 48 to discharge the gas flow 30 towards the first stage vanes 44 and first stage blades 46.
In operation, the compressor section 12 receives air through an intake (not shown) and compresses it. The compressed air enters the chamber 30 in the combustion section 14 and is distributed to each of the combustors 32. In each combustor 32, the fuel 34 and compressed air are mixed and burned. The hot, compressed gas flow 30 is then routed through the transition duct 38 to the turbine section 16. In the turbine section 16, the hot, compressed gas flow is turned by the vanes, such as the first stage vane 44, and rotates the blades, such as the first stage blade 52, which in turn drive the rotor assembly 18. The gas flow is then exhausted from the turbine section 16. The turbine system 10 can include additional exhaust structure (not shown) downstream of the turbine section 16. The power thus imparted to the rotor assembly 18 can be used not only to rotate the compressor section blades 26 but also to additionally rotate other machinery, such as an external electric generator or a fan for aircraft propulsion (not shown).
For a better understanding of the invention, a coordinate system can be applied to such a turbine system to assist in the description of the relative location of components in the system and movement within the system. The axis of rotation of the rotor assembly 18 extends longitudinally through the compressor section 12, the combustion section 14 and the turbine section 16 and defines a longitudinal direction. Viewed from the perspective of the general operational flow pattern through the various sections, the turbine components can be described as being located longitudinally upstream or downstream relative to each other. For example, the compressor section 12 is longitudinally upstream of the combustion section 14 and the turbine section 16 is longitudinally downstream of the combustion section 14.
The location of the various components away from the central rotor axis or other longitudinal axis can be described in a radial direction. Thus, for example, the blade 46 extends in a radial direction, or radially, from the rotor disc 50. Locations further away from a longitudinal axis, such as the central rotor axis, can be described as radially outward or outboard compared to closer locations that are radially inward or inboard.
The third coordinate direction—a circumferential direction—can describe the location of a particular component with reference to an imaginary circle around a longitudinal axis, such as the central axis of the rotor assembly 18. For example, looking longitudinally downstream at an array of turbine blades in a turbine engine, one would see each of the blades extending radially outwardly in several radial directions like hands on a clock. The “clock” position—also referred to as the angular position—of each blade describes its location in the circumferential direction. Thus, a blade in this example extending vertically from the rotor disc can be described as being located at the “12 o'clock” position in the circumferential direction while a blade extending to the right from the rotor disc can be described as being located at the “3 o'clock” position in the circumferential direction, and these two blades can be described as being spaced apart in the circumferential direction. Thus, the radial direction can describe the size of the reference circle and the circumferential direction can describe the angular location on the reference circle.
Generally, the longitudinal direction, the radial direction and the circumferential direction are orthogonal to each other. Also, direction does not necessarily connote positive or negative. For example, the longitudinal direction can be both upstream and downstream and need not coincide with the central axis of the rotor. The radial direction can be inward and outward, and is not limited to describing circular objects or arrays. The circumferential direction can be clockwise and counter-clockwise, and, like the radial direction, need not be limited to describing circular objects or arrays.
Further, depending on the context, the relevant position of two components relative to each other can be described with reference to just one of the coordinate directions. For example, the combustor 32 can be described as radially outboard of the blade 46 because the combustor 32 is located radially further away from the central axis of the rotor assembly 18 than the blade 46 is—even though the combustor 32 is not in the same longitudinal plane of the blade 44, and in fact, is longitudinally upstream of the blade 44 and may not be circumferentially aligned with a particular blade.
The coordinate system can also be referenced to describe movement. For example, gas flow 36 in the transition 38 is shown to flow in the direction of arrow 36. This gas flow 36 travels both longitudinally downstream from the combustor 32 to the turbine section 16 and radially inward from the combustor 32 to the first stage vanes 44 and blades 46.
In the context of describing movement, such as the flow of a gas, the circumferential direction can also be referred to as the tangential direction. When gas flows in the circumferential direction, a component of the flow direction is tangential to a point on the circular path. At any given point on the circle path, the circumferential flow can have a relatively larger tangential component and a relatively smaller radial component. Since the tangential component predominates, particularly for larger diameter paths, such as around vane and blade arrays in a turbine engine, a circumferential direction and tangential direction can be regarded as substantially the same.
Bearing this coordinate system in mind and referring to FIG. 2, a transition duct 54 is shown alone as it would be seen when viewed from longitudinally downstream. This particular transition duct 54 is oriented in the 12 o'clock circumferential position and it should be understood that a turbine engine would have additional transition ducts, for example, a total of sixteen, spaced in an annular array.
The transition duct 54 can include a transition duct body 56 having an inlet 58 for receiving a gas flow exhausted by an associated combustor (not shown, but see FIG. 1). The transition duct body 56 can include an internal passage 60 from the inlet 58 to an outlet 62 from which the gas flow is discharged towards the turbine section (not shown). Because the combustor is radially outboard of the first stage of the turbine section (see FIG. 1), the transition duct 54 extends radially inwardly from its inlet 58 to its outlet 62. In FIG. 2, this radial direction is depicted by the axis 64. The transition duct 54 includes a longitudinal bend 66 near the outlet 62 to discharge the gas flow predominantly longitudinally. Because the gas flow in the transition duct 54 is redirected radially inwardly and then longitudinally, the transition duct 54 experiences substantial bending thrust in the radial direction 64. This radial thrust pushes the outlet region of the transition duct 54 radially outwardly (up in the plane of the page of the figure). To support the transition duct 54 against this bending thrust, the transition duct 54 can be radially supported by various braces (not shown) at its ends, as it well known in the art.
It can be seen that the outlet 62 and the inlet 58 are aligned along the circumferential or tangential direction, which is depicted by the axis 68. Thus, while the transition duct 54 routes the gas flow longitudinally downstream and radially inwardly, there is essentially no flow routing in the circumferential or tangential direction.
Reference is now made to FIG. 3, focusing on a turbine subsection 70 that includes a combustor 72, a transition duct 74 and first stage vanes 76 and blades 78. FIG. 3 shows a view from above of the combustor 72, the transition duct 74, a few first stage vanes 76 and a few first stage blades 78, illustrated schematically. It should be understood that in a turbine, there would be additional first stage vanes spaced apart circumferentially to form an annular array. Similarly, there would be additional first stage blades spaced apart circumferentially to form an annular array. These additional vanes and blades are not shown in FIG. 3 to facilitate illustration. This schematic illustration is also not intended to be to scale. A turbine system would typically also include additional combustors and transitions, but a single combustor 72 and transition 74 are shown schematically for purposes of illustration.
From this top view, the longitudinal direction can be noted by reference to the axis 80. The circumferential or tangential direction can be noted by reference to the axis 82. The radial direction is not illustrated because the radial direction lies into and out of the page of the figure, but would be generally orthogonal to the longitudinal direction and the radial direction.
Gas flow, such as hot, compressed gas with perhaps some limited liquid content, is exhausted from the combustor 72 and routed by the transition duct 74 to the first stage vanes 76 and blades 78. The gas flow as discharged from the exit or outlet 86 of the transition duct 74 generally travels downstream in the longitudinal direction, as indicated by the arrow 84. There may be some incidental, small-scale radial and circumferential flow components to the discharged gas flow due to edge conditions 86 at the outlet and other factors. However, such side flow should be regarded as relatively de minimis compared to the overall flow direction, which is predominantly longitudinal, particularly in the central region of the flow away from the edges.
As this longitudinal gas flow 84 discharges from the outlet 86 of the transition duct 74, the flow passes the first stage vanes 76. The function of the first stage vanes 76 is to accelerate and turn the predominantly longitudinal flow in the circumferential direction 82 so that the predominant flow direction of the gas flow leaving the trailing edges of vanes 76 is angled in the circumferential or tangential direction relative to the longitudinal direction as shown, for example, by the arrow 88. This turned flow 88 thus has a longitudinal component and a circumferential component. The flow angle can be substantial, in the range of 40 degrees to 85 degrees measured from the longitudinal axis 80. By accelerating and angling the gas flow in the circumferential direction 82 relative to the longitudinal direction 80, the resulting gas flow 88 more effectively imparts its energy to the first row blades 78, which in turn rotate the associated rotor assembly (not shown).
The use of first stage vanes to accelerate and turn the longitudinal gas flow in the circumferential direction present several challenges. The vanes and the associated vane support structure (see FIG. 1) must have high strength characteristics to withstand the forces generated in changing the direction of a extremely hot, high pressure gas flow over a substantial angle in a relatively short distance. The temperature of the gas flow and the heat generated by this turning process also require a vane cooling system. The forces and heat involved can crack and otherwise damage the vanes and associated support structure. To address these various requirements and operating conditions, the first stage vanes and the associated support structure and cooling systems have developed into a complex system that can be expensive to manufacture, install, and, in the event of damage, repair and replace.
Thus, there is a need to accelerate and tangentially turn a gas flow for presentation to a first stage blade array without the complications and related costs and damage risks associated with first stage vanes.